The present invention relates to decelerating an aircraft and, in particular, to a method of applying a braking force to the wheel of an aircraft and to a braking apparatus for performing such a method.
After having touched-down on landing, an aircraft is caused to decelerate in various ways, one example of which being by means of application of a braking torque to the wheels of the aircraft. It is desirable to decelerate the aircraft in an efficient and controlled manner. Thus, it is desirable to maximise the pilots demand for deceleration of the aircraft by means of the braking torque applied to the wheels. The wheels of the aircraft are prone, when subjected to a sufficient braking torque, to skidding and may, in severe cases, lock-up completely. It will be appreciated that there is generally some slip between the wheels and the ground when the aircraft is moving, but that above a given amount of slip the wheels can be considered as skidding. When the wheels are skidding the ability of the aircraft to decelerate by application of the brakes is impaired. Aircraft are therefore commonly provided with anti-skid systems.
A known aircraft anti-skid system for a single wheel of an aircraft monitors various parameters including, in particular, the rotational speed of the wheel and the speed of the aircraft. From the measured values of the rotational speed of the wheels and the speed of the aircraft, and from knowing the rolling radius of the wheel, the amount of slip, λ, may be calculated from the equation:λ=1−ωR/V, where    ω=the rotational speed of the wheel,    R=the rolling radius of the wheel, and    V=the speed of the aircraft.
If the slip λ increases above a given threshold indicating that the aircraft has started skidding, the braking torque is reduced until the slip has decreased below the threshold. The known system suffers from certain disadvantages. In particular the system tends to be reactive as opposed to being proactive. For example, the system allows the wheels to skid before reducing the braking torque.